The present invention relates generally to flowmeters, and more particularly, to ultrasonic flowmeters.
Water meters to measure flow rate or velocity of a fluid inside a pipe are abundant and diverse and are available from many manufacturers. The most popular and least expensive are the turbine meters. These meters can cover two orders of magnitude in flow, e.g., 0.2 gal/min to 20 gal/min. One drawback of many meters including the turbine meters is that installation of the meters requires that the pipe carrying the fluid to be measured must be cut to place the measuring device inside the pipe. This installation oftentimes has associated labor costs that are greater than the cost of the meter itself. Other problems with such in-flow meters include the tendency for the meters to become clogged and their calibration to deteriorate over time.
Non-invasive water meters have addressed the installation problems caused by others meters. The most common type of non-invasive water meter uses ultrasonic pulses. The ultrasonic pulses are sent both downstream and upstream relative to the flow of the fluid within the pipe. The difference in time required to travel upstream versus downstream is then used to determine the velocity of the fluid flowing within the pipe. These ultrasonic meters, however, are very expensive. Typically, a single meter costs between $5,000 and $10,000. This high expense limits the scope of application for these non-invasive meters. A main factor in this large expense is that considerable resources are devoted to ensuring accuracy of the flow rate and fluid velocity measurement.
Unfortunately, prior art flowmeters have limited success in producing accurate measurements. There are many factors influencing flow rate and fluid velocity measurement. However, prior art meters can only inherently account for variation in a small number of the factors. The factors influencing flow rate and fluid velocity measurement include changes in acoustic velocity of the measured fluid due to causes such as temperature changes, turbulence, mixing with gases or particulate, or changes in fluid type. Acoustic velocity of the ultrasonic pulse traveling through the material of the pipe and transducers involved can also vary as the materials used vary in different applications. Other factors influencing flow rate and fluid velocity measurement relate to the distances traveled by the ultrasonic pulses. Variation in these distances depend on factors such as changes in inside pipe diameter due to pipe construction, sludge built-up inside the pipe, pipe wall thickness, or placement of the transducers. Additional factors are associated with the electronics used such as timer accuracies and electronic delays.
The prior art approaches may address variability resulting from a few of the factors. However, fundamentally, the prior art approaches are not constructed to deal with variability in a wide range of factors involved in obtaining a measurement. Thus, the prior art approaches select a limited number, such as one or two, of the factors and arrange complicated and expensive schemes to compensate for variability in the selected factors. What is missing in the prior art systems and methods of measuring flow rate and fluid velocity are inexpensive, noninvasive meters that account for variability in a wide range of factors, including those mentioned, and that are adaptive for additional factors later added. Accounting for variability in all factors that influence measurement of flow rate and fluid velocity would produce more consistently accurate flow rate and fluid velocity measurements in a wide variety of environments. The present invention fulfills these needs and further provides other related advantages.
The present invention resides in an ultrasonic system for fluid contained within a pipe. The ultrasonic system includes upstream and downstream transducers mountable on the pipe. The transducers are configured to receive ultrasonic pulses.
The ultrasonic system further includes a processor having a timer and a counter. The processor is configured to use the timer and counter to determine a time period, TU, associated with a first number of ultrasonic pulses received by the upstream transducer. The processor is further configured to use the timer and counter to determine a time period, TD, associated with a second number of ultrasonic pulses received by the downstream transducer. The processor is configured to determine at least one characteristic of the fluid or the pipe based on TU and TD and based on a filter system. In one aspect of the invention the filter system comprises at least one linear filter wherein one of the at least one linear filter includes a coefficient, a1, for a term of a1*TU, and a coefficient, a2, for a term of a2*TD, the coefficients a1 and a2 not being equal to one another. In another aspect of the ultrasonic system, the filter system comprises at least one non-linear filter. In a further aspect of the ultrasonic system, the filter system comprises at least one neural network.
Further aspects of the ultrasonic system include filter systems having parameter filters and validation filters. The filter systems may also further include filter coefficients based on variability in at least one of piped diameter, acoustic fluid velocity, differential offset errors, and common offset errors.